Atomic clocks can be implemented as extremely accurate and stable frequency references, such as for use in aerospace applications. As an example, atomic clocks can be used in bistatic radar systems, Global Navigation Satellite systems (GNSS), and other navigation and positioning systems, such as satellite systems. Atomic clocks can also be used in communications systems, such as cellular phone systems. Some cold atom sources can include a magneto-optical trap (MOT). A MOT functions by trapping alkali metal atoms, such as cesium (Cs) or rubidium (Rb), in an atom trapping region, and may be configured such that the atoms are confined to a nominally spherical region of space. As an example, an atomic clock can utilize a cold atom source that traps the alkali metal atoms that can transition between two states in response to optical interrogation to provide frequency monitoring of the optical beam. Thus, the cold atoms can be implemented as a frequency reference, replacing the more typical hot atom beam systems which take up significantly more space for the same performance.